Carboxylic esters infrared absorptions

The teichoic acid shows an infrared absorption band at 1751 cm.-1, characteristic of carboxylic ester groups, which is not observed in samples from which the D-alanine residues have been removed. Removal of the u-alanine was readily effected with ammonia or hydroxylamine, when D-alaninamide or D-alanine hydroxamate were formed. The kinetics of the reaction with hydroxylamine reveal the high reactivity of its D-alanine ester linkages, which, like those in most other teichoic acids, are activated by the presence of a neighboring phosphate group. That the D-alanine residue is attached directly to the ribitol residues, instead of to the d-glucosyl substituents, was also shown by oxidation with periodate under controlled conditions of pH, when it was found that the D-alanine residues protect the ribitol residues from oxidation. Under the same conditions, all of the ribitol residues were oxidized in a sample of teichoic acid from which the D-alanine had been removed, and it is concluded that the ester groups are attached to C-2 or C-3 of the ribitol residues. 

The use of nitrogen dioxide for the selective oxidation of polysaccharides to polyuronic acids was introduced by Kenyon and his coworkers13,63 in 1941. By this means extensive oxidation of the primary alcohol groups in cellulose was obtained, through the mechanism of preferential nitration followed by decomposition of the nitric acid ester with carboxyl forma-tion.68(0< > Apparently some undissociated nitration products also were formed, since infrared absorption studies54 indicated the presence of nitrate radicals in the polyuronic acid. Side reactions produced carboxyl,... 

Infrared absorption spectral data for several oxazole derivatives,86 90 including alkyl-98 186 and aryl-263 264 substituted oxazoles, 2-amino- and substituted-amino derivatives109 112 136, 5-amino179 198-201 and 5-alkoxy-oxazoles,66 carboxylic acids,112 147 esters,126 179 184 carboxamides,199 200 4-acetyloxazoles,147 halogenoalkyl oxazoles,91 oxazolines,262 and benzoxazoles262 have been reported. 

Ludwig. This compound has an empirical formula corresponding to structure (1) and shows the ultraviolet and infrared" absorptions of a pyrrole-3-carboxylic ester. Its acetylation gives a tetra-O-acetyl derivative." Oxidation with lead tetraacetate yields ethyl 5-formyl-2-methyl-pyrrole-3-carboxylate (4), identical with the compound prepared in a different way. Oxidation with potassium permanganate in alkaline solution at low temperature yields 3-(ethoxycarbonyl)-2-methylpyrrole-5-carboxylic acid (7) which can be transformed " into the diethyl ester (8), identical... 

Aldehydes Amides Carboxylic acid anhydrides Carboxylic acids Esters Ketones and functional groups, 56 infrared absorption frequencies, 519,... 

FT-IR spectra (9) of pectin/starch/glycerol (P/S/G) films were taken to provide information concerning the microstructure around ester and carboxylic acid side chains in the backbone of pectin. Pectin, unlike starch and glycerol, exhibits infrared absorption bands in the regions near 1610 and 1740 cm For pectin dissolved in D2O, absorption bands occur at about 1730, 1740, and 1607 cm. These arise from the carboxylic acid C=0 stretching band, the methyl ester C=0 stretching band, and iht antisynunetric COO stretching band, respectively. The carboxylic acid band overlaps the ester band sufficiently that these appear as one broad band (22). 

Analyses of the chloroform-soluble extracts of the subbituminous coal by Fourier transform infrared spectroscopy (FTIR) showed the presence of a sharp carbonyl absorption peak (1800-1650 cm ) in the extracts from the parent coal and in those obtained at yields less than about 10% wt dmmf. The peak, which is attributed to ketones and carboxylates, disappeared at higher conversions (16). Whitehurst and co-workers (12) established that carbonyl- containing compounds, such as esters and carboxylates, can cleave under thermal treatment to produce CO, CO2 and phenols. They concluded that the evolution of these gases during coal liquefaction could originate from the decomposition of similar oxygen functionalities in the coal. 

IR monitoring of oxidation process. Monitoring lubricants by infrared spectroscopy is a well established technique. The infrared spectra of oxidized (used) engine oil samples can be split into three parts (a) above 1900 cm 1, (b) 1900 to 1500 cm 1, and (c) below 1500 cm"1. The spectral changes in the region between 1900 to 1500 cm 1 in commercial automotive oils (SAE 10W/40, API service SE) operated in a Toyota 20R engine over a 8000 km period were evaluated (Coates and Setti, 1984). Major absorptions bands (1900 to 1500 cm 1) of the spectra are [cm 1] 1732 (oxidation, carbonyl esters), 1710 (oxidation, carbonyl ketones/acids), 1629 (nitrate esters), 1605 (carboxylates) of used oils. 

After fabrication, the ester type films are hydrolyzed in a caustic solution to be converted to carboxylic acid type membranes. Figure 6 shows the change of infrared spectrum by hydrolysis of the ester type film in 25 wt% caustic solution at 90°C for 16 hrs. Complete hydrolysis is indicated by the fact that the absorption at 1780 cm l due to Vc=0 (-COOCH3) is wholly shifted to 1680 cm l of vc=0 (-COONa). 

Fourier Transform Infrared (FTIR) spectroscopy show s a strong absorption at 1735 cm , a spectrum tyq)ical for cellulosic acid. When the sodium salt of oxidized cellulose is isolated and measured, a strong carboxylate band is seen at 1594 cm T In addition to the carboxylate band a small band (approximately 2% intensity) is uncovered at 1737 cm . This absorption may correspond to a strained ester or lactone moiety (unpublshed Zhbankov RG, 1991). 

Esters are carboxylic acid derivatives, and the spectrum of ethyl acetate is shown in Figure 14.19D. The carbonyl absorption does not distinguish this compound from an aldehyde or a ketone, but there is the C-O absorption at about 1200 cm 1. Because this is in the fingerprint region, however, its position can be difficult to identify. This is clearly the case for methyl pentanoate, where the C-0 absorption can easily be missed or misidentified. Based only on the infrared, it may be difficult to distinguish an ester from an aliphatic aldehyde or ketone. If the formula is known, however (from mass spectrometry), the identification is easier because an ester has two oxygen atoms, whereas the aldehyde or ketone has only one. 

To one skilled in the interpretation of infrared spectra, the absorption patterns can yield an enormous amount of information about chemical structure. However, we have neither the time nor the need to develop this level of competence. The value of infrared spectra for us is that they can be used to determine the presence or absence of certain functional groups. A carbonyl group, for example, typically shows strong absorption at approximately 1630-1820 cm" The position of absorption for a particular carbonyl group depends on whether it is an aldehyde, a ketone, a carboxylic acid, or an ester if it is in a ring, the position of absorption depends on the size of the ring. In this chapter, we discuss how structural variations, such as ring size or other factors, affect this value. 

A suitable method for determining the anhydride group is titration with aqueous potassium hydroxide in pyridine after previous esterification of the carboxyl group with diazomethane. This esterification is carried out in diethyl ether methanol (9 + 1). After methylation, which takes about 10 minutes for 0.5 g of sample, the solvents are removed by evaporation and a portion of the derivatised polymer is dissolved in pyridine and titrated. In the infrared spectra of the resin before and after methylation it can be seen that the absorption band of the acid group at 5.84 i,m disappears and a carbonyl band of the ester at 5.74 p,m is formed. The acid content of the sample is found from the difference in titres of an immethylated and a methylated product. 

Simple esters have an absorption at about 1740 cm, a higher wavenumber than aldehyde and ketone absorptions. Esters also have a C—O stretching absorption in the 1000—1300 cm" region. Because other absorptions also occur in this region, such data are useful only as a confirmation when an ester is suspected from other data such as the carbonyl stretching absorption. We recall that alcohols, ethers, and carboxylic acids have C—O absorptions in the same region. Figure 2.14 shows the infrared spectrum of ethyl acetate. 

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